BOISE, Idaho — Faced with sexual harassment allegations, Republican Sen. John McGee was given two choices: Quit or go before a state Senate ethics panel.

The 39-year-old, four-term lawmaker opted to resign Wednesday, capping a political free-fall that began last year with a Father's Day drunken driving and car theft arrest.

His political demise came swiftly.

Senate President Pro Tem Brent Hill and Majority Leader Bart Davis were told of confidential allegations by a young woman on McGee's staff on Saturday. On the counsel of other Senate employees, the woman on Monday delivered the allegations to Hill and Davis in person.

Hill, R-Rexburg, said he told McGee that if he didn't step down he would face a protracted, potentially damaging Senate ethics panel investigation.

"My first priority is to ensure the safe secure and professional work environment of the senate employees," Hill said after meeting with the Senate GOP caucus. "My second priority is to protect the integrity of the institution."

Hill did not share details of the allegations, but the Idaho attorney general's office is investigating the claims. Hill also did not identify the accuser, saying he wanted to protect her privacy. The Senate aide was reassigned and allowed to take paid leave.

McGee, the fourth-ranking member of the chamber, submitted his resignation letter Wednesday morning but did not acknowledge any wrongdoing, Hill said.

McGee, who was absent from the Capitol on Wednesday, did not immediately return telephone messages.

"It's been my pleasure and honor to serve the citizens of District 10 in the Idaho State Senate for the past eight years," McGee said in his two-paragraph resignation letter.

Gov. C.L. "Butch" Otter declined to comment on McGee's departure.

McGee is also the chairman of the Canyon County Republican Party.

Idaho State Republican Party director Jonathan Parker said Wednesday he hasn't received a resignation letter for that post. Canyon County GOP vice-chairman Steve Kren couldn't be reached for comment.

This June 19, 2011 photo provided by the Ada County Sheriff's office shows Idaho Sen. John McGee in Boise Idaho. Idaho Senate President Pro Tem Brent Hill announced McGee has resigned amid allegations of sexual harassment of a female senate aide during a news conference at the Idaho Capitol in Boise, Idaho on Wednesday. Feb. 22, 2012. (Ada County Sheriff's Office, Associated Press)

McGee's exit left senators from both parties shaking their heads in the basement hallway of the Capitol.

Minority Democrats said they were shocked.

"Whenever any of our members has this happen, it's sobering," said Michelle Stennett, D-Ketchum. "It's a sad day for the Senate."

McGee rose quickly and had been considered a candidate for higher elected office. His resignation would seem to put an end to any such aspirations.

The departure caps a disastrous run for McGee, who was arrested on June 19 — Father's Day. McGee has said he began drinking at a Boise golf tournament, and says he blacked out and doesn't remember the details of what happened next.

According to police, McGee took a Ford Excursion and cargo trailer from the southwest Boise home of a "complete stranger" and got it stuck in a yard. A breath test showed McGee's blood-alcohol content at nearly twice the legal limit.

Last summer, McGee pleaded guilty to drunken driving in a deal that erased accompanying auto theft charges. He served jail time and paid restitution for a stranger's vehicle that he damaged.

McGee's reputation was further bruised over the summer when the AP reported that despite having a home just 26 miles from the Capitol, he had been claiming a $122 per diem during the Legislature that adds up to some $6,000 annually. The money is meant to defray the cost of a second residence in Boise, but McGee was spending nights at his parents' house in Boise.

Most southwestern Idaho lawmakers claim a $49 per diem.

State Democratic Chairman Larry Grant said McGee's resignation was appropriate, given all that's happened.

"The veracity of the claim against McGee is yet to be fully evaluated," said Grant, , in a statement. "However, he has already provided high-profile proof of his lack of judgment with his arrest over the summer of drunk driving, stealing a vehicle and questionable claims on his legislative per diem payments."

At the start of the 2012 session, McGee apologized to his colleagues for his actions and survived efforts calling for him to step down from his leadership post.

At least nine senators, concerned that their constituents thought the vote was unanimous, issued a public letter saying they favored McGee's ouster.

One of those was Senate Assistant Majority Leader Chuck Winder, R-Meridian. At Wednesday's press conference, Winder said the allegations against McGee were no cause to gloat.

"No one is saying I told you so," Winder said. "We had made our point, that it wasn't unanimous. We had moved on, we were all working well together, and honestly, this fell out of the sky."